| Mini core collection is a core of the core collection and a representative subset of core collection,consisted of1imited accessions with minimum genetic redundantcy and retained most genetic diversityand genetic structure in initial collection. The ultimate goal of constructing mini core collection of to-bacco is to study its genetic diversity, promote its effective management, deeply evaluation and makingfull use of, thus it will meet the needs of production and scientific research to the greatest degree. Accu-rate measure in genetic similarity among accessions and specifying an appropriate samlpling stratey is akey step in developing a mini core collection. This study will focus on evaluating the properties of dif-ferent integrating ratio between molecular marker and quantitative trait and different sampling strategiesby comparing the genetic variation captured by subsets of tobacco, setting up a mini core collection oftobacco. Two accessions of flue-cured tobacco belong to mini core collection were screened to sudy theinheritance of important botany and physiological traits with the joint segregation analysis method ofmixed major gene plus polygene genetic mode, so as to provide some theoretical guidance for the quan-titative genetic breeding of flue-cured tobacco. The main conclusions of this study were as follows:(1)The conception of core primer was defined.12different tobacco accessions was used to screen700SSR primer pairs which were equally distributed in24linkage groups of tobacco, and finally54core primer pairs fitting for tobacco DNA fingerprint pool were screened. Here we publish54core pri-mer pairs and their polymorphic information, which will be helpful to regulate the procedure and pro-mote the efficiency for screening SSR primers, and will play an important role in tobacco genetic diver-sity evaluation, core collection construction, fingerprint construction, seed genuineness and purity iden-tification of the tobacco varieties.(2)446accessions of tobacco core collection which were constrcted in2001were characterized by23agronomic traits and molecular markers on54SSR core primers to establish a mini core collection.Seven different sampling ratios of accessions were tested, including5%to40%with an interval of5%.The results showed that15%and30%of samples could conserve more than90%and80%of variationsin N.tabacum and N.rustica respectively, which indicated that15%and30%was an adequate samplingratio for establishing the mini core collection in N.tabacum and N.rustica respectively. The intergratingdata between quantitative and molecular data is better than each other, and the proportion of quantitativeand molecular data for0.1:0.9was optimal. A comparision of the efficiencies of two genetic distance(Euclidean distance and Mahalanobis distance) for the continuous data and foue genetic distance (Sim-ple matching, Jaccard, Nei-Li and Principal component distance), showed that Euclidean distance andJaccard were optimal genetic distance. A comparison of the efficiencies of four sampling strategies bygeographical grouping (proportional, square root, logarithmic, and genetic diversity-depend) and threesampling mehtods (random sampling, preferred sampling and maximization), indicated proportional andlogarithmic strategy was optimal in term of establishing the most representative mini core collection,when the quantity of samples to be located is significant, the former is better, whereas the latter is better. Thus, a mini core collection of127accessions, including117selected based on proportional and loga-rithmic strategy and10accessions selected by their specific agro-morphological traits, was constructed.The tests on SSR data and agro-morphological characters demonstrated that the mini core collection hashigh genetic diversity and a good representative to the entire collection.(3)The joint segregation analysis method of mixed major gene plus polygene genetic model wasused to study the inheritance of important botanical traits in flue-cured tobacco. Six generations（P1, P2,F1, B1, B2and F2） from the crosses （Wanye×Coker319） were investigated. It was found that plantheight, leaf number, leaf area and fresh leaf weight in flue-cured tobacco appeared to be a quantitativetrait and their inheritances fitted to a mixed genetic model of two major genes with addi-tive-dominant-epistatic effects plus polygenes with additive-dominant-epistatic effects （E0model）.Plant height and leaf number was chiefly controlled by the additive effect and the epistatic effect of do-minance×dominance. The additive, dominant and epistatic effects which the epistatic effect> the addi-tive effect> the dominance effect of leaf area and fresh leaf weight were all important. Heritabilities ofthe major genes were estimated to be57.53%,42.63%,30.32%and44.26%in F2. The inheritance ofdays of transplanting to flowering fitted to a mixed genetic model of two major genes with addi-tive-dominant-epistatic effects plus polygenes with additive-dominant effects （E1model） and it wasmainly dominated by the epistatic effect of additive×additive, the additive effect, and the epistatic ef-fect of dominance×dominance, the heritability of the major gene was64.79%in F2. The inheritance ofstem girth and leaf mass per area fitted to a mixed genetic model of one major gene with complete do-minant effects plus polygenes with additive-dominant effects （D3model）, stem girth was principallycontrolled by polygenes which additive effect was equal to its dominance effect, the heritability of themajor gene was2.48%and38.71%in F2. The inheritance of leaf index fitted to a mixed genetic modelof one major gene with additive-dominant effects plus polygenes with additive-dominant-epistatic ef-fects （D0model）, the additive effect and the dominance effect of the major gene was almost equal, theheritability of the major gene was49.64%in F2. Leaf length, leaf width, internodal distance and capsuleweight fitted to a mixed genetic model of polygenes with additive-dominant-epistatic effects （C0model）, the heritability of the polygenes were60.75%,62.14%,75.08%and82.34%in F2.(4)The mixed major-gene plus polygene inheritance model in six generations （P1, P2, F1, B1, B2,and F2）was used to analyze the inheritance of several physiological traits in the flue-cured tobacco（N.tabacum） cross between WANYE and Coker319. The results showed that the SPAD reading wascontrolled by one gene with additive-dominance effect plus polygenes with addi-tive-dominance-epistatic effect （D0model）. The additive effect for major gene was-5.89, the do-minant effect for major gene was-3.47. The major gene heritabilities in B1, B2and F2were3.61%,46.11%and48.94%, respectively, and the corresponding polygenic heritabilities were52.04%,8.25%and0.00%, respectively. These results indicated that major gene in F2was a key factor and environment fac-tor was also relatively important. This implies that in the genetic improvement of SPAD reading ma-jor-gene is a main factor whereas environmental effect should be taken care of. Photosynthetic rate andtranspiration rate fitted to a mixed genetic model of polygenes with additive-dominant-epistatic effects （C0model）, the heritability of the polygenes were20.69%and13.56%in F2. It was also found thatstomatal conductance in flue-cured tobacco appeared to be a quantitative trait and their inheritances fit-ted to a mixed genetic model of two major genes with additive-dominant-epistatic effects plus poly-genes with additive-dominant-epistatic effects （E0model）. Stomatal conductance was chiefly con-trolled by the epistatic effect of dominance×dominance. Heritabilities of the major genes were esti-mated to be58.03%,35.11%and40.59%in B1, B2and F2, and the heritabilities of the polygenes wereestimated to be1.43%,21.34%and2.03%in B1, B2and F2. |
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